Mycobacterium tuberculosis (MTB) is probably the most ubiquitous microbial pathogen in the world today infecting one-third of the total population and causing millions of active tuberculosis (TB) cases each year. The economic costs are substantial and more than one million people die of TB infections each year. Before the arrival of antimicrobial therapy, TB was one of leading causes of human deaths with high mortality rates common in untreated cases of active TB infections. With the discovery of effective drugs against the disease, it became possible to cure the illness. However, antimicrobial resistance has been rising over time. Multidrug-resistant (MDR) and now extensively drug-resistant (XDR) strains that resist most first-line and second-line agents are appearing that are difficult to successfully treat. The isothiazoloquinolone (ITQ) ACH- 702 was shown to have antibacterial activity against both non-dividing and biofilm staphylococci and to be active against MTB including MDR/XDR strains with minimum inhibitory concentrations (MICs) of 1 5g/mL or less. These data suggested the potential of ITQs in shortening the duration of treatment for susceptible strains, in killing latent MTB in the host, and in effective therapy for MDR/XDR strains. However, ACH-702 was found to have suboptimal pharmacokinetic (PK) properties that precluded development as an oral agent. A prototype analog ACH-0141998, a hydroxythienoquinolone (HTQ), demonstrated improved metabolic stability and suggests a path forward to further analogs with better safety profiles and PK properties capable of supporting oral dosing. In Phase I, we will generate a series of HTQ analogs and evaluate them in a series of in vitro assays and select candidates for further advancement. The ultimate goal of this Phase I proposal is to identify a compound(s) that has metabolic stability and improved antibacterial activity against MTB including MDR/XDR strains. In Phase II, we will initiate in vivo testing including PK studies, acute and repeat-dose animal toxicity studies, and assessment of effectiveness in animal models. PUBLIC HEALTH RELEVANCE: Mycobacterium tuberculosis (MTB) is a major global health concern. The spread of multidrug-resistant MDRTB isolates threatens to undermine our ability to treat these infections. The overall goal of this project is to identify antimicrobial compounds that have the potential to successfully treat both wild-type and MDRTB isolates.